1. Field of the Invention
The present invention relates to a coating solution for forming a colored thin film as well as a colored thin film, a colored antistatic film, a colored low reflection (i.e., anti-reflective) film or a colored low reflection antistatic film obtainable by coating such a coating solution on e.g. a face panel of a cathode ray tube, and a method for its production.
2. Discussion of Background
With respect to a method for coating an antistatic film, a colored thin film, a colored antistatic film, a low reflection antistatic film or a colored low reflection antistatic film, many studies have been made not only on optical equipments but also on consumer equipments, particularly cathode ray tubes (CRT) for televisions or computer terminals.
With respect to antistatic treatment, for example, Japanese Unexamined Patent Publication No. 76247/1988 proposes a method of forming conductive oxide layers of e.g. tin oxide and indium oxide by a CVD method by heating the panel surface of a cathode ray tube at a temperature of about 350.degree. C.
With respect to coloring the film, Japanese Unexamined Patent Publication No. 275664/1989 proposes a method of using a water-soluble phthalocyanine compound. Further, with respect to a colored thin film having an antistatic performance, Japanese Unexamined Patent Publication No. 251545/1989 discloses an antistatic film employing methyl violet.
With respect to low reflectance, it has been common, for example, to provide a SiO.sub.2 layer having fine roughness on the surface in order to provide an anti-glare effect to the surface of the face panel of the cathode ray tube as disclosed in Japanese Unexamined Patent Publication No. 118931/1986, or to provide surface roughness by etching with hydrofluoric acid. However, such a method is so-called non-glare treatment to scatter exterior lights and is not essentially a means to provide a low reflection layer, whereby reduction of the reflectance is rather limited, and in the case of a cathode ray tube, such tends to cause a deterioration of the resolution.
With respect to a low reflection antistatic film, Japanese Unexamined Patent Publication No. 93136/1991 discloses a method of forming an optical multi-layer film by an ion plating method.
Among the above-mentioned methods, the technique to form an antistatic film by a CVD method has not only a drawback that a high cost is required for the apparatus but also a problem that since the face plate of the cathode ray tube is heated at a high temperature, the phosphor in the cathode ray tube tends to fall off, and the dimensional precision tends to deteriorate. In such a case, a high temperature at a level of 400.degree. C. is usually required, and there has been a problem that if baking is conducted at a low temperature, a film having a sufficiently low resistance can hardly be obtained.
The above-mentioned method in which a water-soluble phthalocyanine compound is employed for the colored thin film, has a drawback that since the organic dye is employed, the film is poor in the heat resistance and weather resistance and has absorption at a certain specific wavelength, whereby it tends to be difficult to obtain uniform absorption over the entire wavelength range of visible lights. For the same reasons, the antistatic film containing methyl violet as disclosed in Japanese Unexamined Patent Publication No. 251545/1989 is poor in the heat resistance and weather resistance and has a difficulty that uniform absorption can hardly be obtained over the entire wavelength range of visible lights.
The ion plating method is not industrially inexpensive, and it is hardly possible to thereby attain uniform absorption over the visible light wavelength range, whereby no improvement of the contrast can be expected when such a film is applied to a cathode ray tube.